Fix validations on child record when record parent has validate: false

Fixes #17621. This 5 year old (or older) issue causes validations to fire
when a parent record has `validate: false` option and a child record is
saved. It's not the responsibility of the model to validate an
associated object unless the object was created or modified by the
parent.

Clean up tests related to validations

`assert_nothing_raised` is not benefiting us in these tests
Corrected spelling of "respects"
It's better to use `assert_not_operator` over `assert !r.valid`

3 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/validations/length.rb b/activerecord/lib/active_record/validations/length.rb
index ef5a6cbbe7..5991fbad8e 100644
--- a/activerecord/lib/active_record/validations/length.rb
+++ b/activerecord/lib/active_record/validations/length.rb
@@ -2,11 +2,23 @@ module ActiveRecord
   module Validations
     class LengthValidator < ActiveModel::Validations::LengthValidator # :nodoc:
       def validate_each(record, attribute, association_or_value)
+        return unless should_validate?(record) || associations_are_dirty?(record)
         if association_or_value.respond_to?(:loaded?) && association_or_value.loaded?
           association_or_value = association_or_value.target.reject(&:marked_for_destruction?)
         end
         super
       end
+
+      def associations_are_dirty?(record)
+        attributes.any? do |attribute|
+          value = record.read_attribute_for_validation(attribute)
+          if value.respond_to?(:loaded?) && value.loaded?
+            value.target.any?(&:marked_for_destruction?)
+          else
+            false
+          end
+        end
+      end
     end
 
     module ClassMethods
diff --git a/activerecord/lib/active_record/validations/presence.rb b/activerecord/lib/active_record/validations/presence.rb
index 61b30749d9..75d5bd5a35 100644
--- a/activerecord/lib/active_record/validations/presence.rb
+++ b/activerecord/lib/active_record/validations/presence.rb
@@ -2,6 +2,7 @@ module ActiveRecord
   module Validations
     class PresenceValidator < ActiveModel::Validations::PresenceValidator # :nodoc:
       def validate(record)
+        return unless should_validate?(record)
         super
         attributes.each do |attribute|
           next unless record.class._reflect_on_association(attribute)
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 8f7a46f2c7..ad56f637e3 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -11,6 +11,7 @@ module ActiveRecord
       end
 
       def validate_each(record, attribute, value)
+        return unless should_validate?(record)
         finder_class = find_finder_class_for(record)
         table = finder_class.arel_table
         value = map_enum_attribute(finder_class, attribute, value)